Rainbow - colours in the eye and on the screen who I am Alan Dix part-time Professor at Lancaster part-time entrepreneur at aQtive and vfridge

Rainbow - colours in the eye and on the screen  play with colours  use of colour  'physics' of colour  how we see colour  how computers do colour see also

play with colours colour is surprisingly complex –physics, aesthetics, psychology using colour can be fun –experiment, play with it! context matters we all see colours differently perception of colour depends on surroundings different at midday or night

the eye of the beholder context matters

good use of colour using conventions (red for alarms etc.) ‘branding’ parts of an interface occasional emphasis redundant coding –i.e. in addition to other means e.g. web link colours - also underlined –for diagrams, etc. yucky clip art, but was all I could find

bad use of colour over use - without very good reason (e.g. kids’ site) colour blindness poor use of contrast do adjust your set! –adjust your monitor to greys only –can you still read your screen?

'physics' of colour ‘colour’ is the wavelength of light like pitch is the wavelength of sound spectrum –from red - longest –to violet - shortest –and beyond … red  infra red (heat)  microwaves  radio violet  ultraviolet ... nasty radiation 7x10 -7 m 4x10 -7 m

mixing colour mixing paint blue + yellow = green (really cyan) mixing lights red + green = yellow called additive and subtractive colour

additive colour - mixing light –physically both colours in the mixed light –like a chord in music –light is really red + green –we see yellow

subtractive - mixing paint –cyan paint absorbs a lot of red –yellow paint absorbs a lot of blue –cyan + yellow absorbs most of the red and blue leaving mainly green light reflected –so we see green

primary colours in music we hear chords and harmony C + G  E there are no primary ‘notes’ in music so why three primary colours? not physics … but the eye

in the eye two types of sensory cells: rods –see black and white and grey –best in low light –good at seeing movement cones –see colours –best in bright light

how we see colour... three types of cones: – red, green and blue! –well nearly... … like 3 radios tuned to different stations –each type sensitive to a range of light frequencies –eye compares ‘response’ of each kind –each mix has same response as some pure colour –3 receptors => 3 dimensions of colour

rods and cones how many –more in the centre (fovea) than the edges => better central vision where they are –cones towards centre, rods towards edge => peripheral vision low-light, good at movement, black and white how fast –black and white faster (in brain) than colour

how computers do colour lots of spots of red, blue and green eye merges them to form colours like pointilist painting colours described using RGB –amount of each colour they have –e.g. #ff00ff = purple

variations different colour models: HSI, CMYK, CIE used for different purposes screen depth –number of bits used per pixel 24 = 8 bits per colour (RGB) = 16 million colours 32 as above, also ‘alpha channel’ (transparency) 16 = 5 bits per colour = ‘thousands of colours’ 8 too few to split, need designed palettes

palettes mapping: 256 colours (8 bits)  selection of full (24 bit) RGB options: –application palettes (why funny things happen!) –system palette (slightly different between platforms) –web colours 6 colour levels for each RGB channel 6x6x6 = 216 combinations of hex 00,33,66,99,cc,ff e.g. #cc3300, #0000ff, #999999

who it was Alan Dix see also